The present invention relates to wastewater treatment systems and processes, and particularly to ecological and biological treatment systems. More specifically, the invention concerns systems and methods for treating wastewater and for using the byproducts of such treatment.
The present invention addresses two critical environmental needs—efficient treatment of wastewater from a variety of sources and development of “green” and renewable energy sources. Wastewater treatment has grown significantly from its origins for treatment of metropolitan sewage. Environmental protection regulations promulgated in the 1900's require treatment of effluent from industrial concerns prior to drainage into a common waterway. Typically, wastewater treatment involves three stages, called primary, secondary and tertiary treatment. First, the solids are separated from the wastewater stream, initially by screens and coarse filters, and then typically by sedimentation or settling within a pre-treatment containment. The separated solids can be removed by skimming (for floating solids) and by sludge scrapers for settled solids.
In the secondary stage, dissolved biological matter is progressively converted into a solid mass by using indigenous, water-borne bacteria. Secondary treatment systems are generally classified as either fixed film or suspended growth. Fixed-film treatment process including trickling filters and rotating biological contactors where the biomass grows on media and the sewage passes over its surface. In suspended growth systems—such as activated sludge—the biomass is well mixed with the sewage and can be operated in a smaller space than fixed-film systems that treat the same amount of water. However, fixed-film systems are more able to cope with drastic changes in the amount of biological material and can provide higher removal rates for organic material and suspended solids than suspended growth systems.
Rotating biological contactors (RBCs) are mechanical secondary treatment systems, which are robust and capable of withstanding surges in organic load. RBCs include rotating disks that support the growth of bacteria and micro-organisms present in the sewage, which breakdown and stabilize organic pollutants. Oxygen is obtained from the atmosphere as the disks rotate. As the micro-organisms grow, they build up on the media until they are sloughed off due to shear forces provided by the rotating discs in the sewage. Effluent from the RBC is then passed through final clarifiers where the micro-organisms in suspension settle as a sludge. The sludge is withdrawn from the clarifier for further treatment
In the tertiary, or final, stage, the biological solids are neutralized for disposal or re-use, and the treated water may be disinfected chemically or physically (for example by lagoons and micro-filtration). The final effluent can be discharged into a stream, river, bay, lagoon or wetland, or it can be used for the irrigation of a golf course, green way or park. If it is sufficiently clean, it can also be used for groundwater recharge. A typical tertiary system may include carbon filters to remove certain toxins, and clarifiers configured to remove other constituents, such as nitrogen and phosphorus. In larger systems, the tertiary stage may incorporate lagooning or discharge into wetlands of engineered reed beds.
The secondary stage of wastewater treatment is notoriously problematic due to the complexity of maintaining large bacterial colonies necessary to biologically treat the wastewater. Maintaining larger and more complex bacterial colonies has unfortunately manifested itself in more costly and complicated equipment and facilities, with a commensurate increase in mechanical failure and equipment downtime. Another potential problem is that the bacterial colonies are intended to convert the wastewater contaminants into other presumably less toxic forms, such as methane, nitric oxide and CO2 gases. Each of these byproducts of bacterial activity is considered to be a greenhouse gas and a contributor in some measure to global warming.
In the 1950s, wastewater treatment strategies were developed that capitalized on the symbiotic relationship between bacteria and algae. Algae produces oxygen necessary for aerobic bacterial growth and bacteria produces CO2 needed for algal growth. The only external input to fuel this symbiotic relationship is sunlight. This strategy was first successfully implemented in open lagoons and wetland treatment facilities. These on-site systems had obvious limitations, such as land space, geography and topography, water clarity, etc. In addition, the on-site systems were prone to algae blooms that would overrun and clog the systems. These limitations led to the development of the algae raceway in the 1970s. The algae raceway is essentially a flume in which nutrient-rich water is allowed to course while exposed to sunlight. The resultant algal biomass is harvested by mechanical means. One significant detriment of the algae raceway is that it requires a large surface area for adequate exposure to sunlight. In addition, the raceway requires a shallow water level to function, which inherently limits the volume and flow of wastewater that can be treated by any particular raceway facility.
The present invention avoids the problems associated with RBCs, open on-site systems and algae raceways.
The second critical environmental need addressed by the present invention is the need for “green” and renewable energy sources. So-called “green” energy sources cause only minimal detrimental impact on the environment. The optimum “green” energy source would produce a net ecological benefit by, for instance, reducing pollutants and re-using waste materials to generate energy or provide a clean energy source.
The need for a renewable energy source has become particularly acute and the subject of widespread concern. For example, fossil-fuel based energy (gas and oil) are known to be finite. While the debate rages as to exactly how finite is “finite”, much evidence suggests that worldwide oil production will peak in around 2010. When the wells will run dry is also hotly debated, but some analysts have suggested that the oil supply will end as early as 2035, while more conservative estimates move the date out to 2060. Nevertheless, there is no question that the fossil fuels will be depleted.
Awareness of the limited life of fossil fuels has prompted significant research and development for renewable energy sources. Much research has been devoted to alternative energy sources, such as solar, wind and wave power. However, these alternative energy sources do not appear to have the near-term capability of satisfying the need for petroleum-type fuels—i.e., gasoline and diesel fuels. Research in the 1980s focused on developing gasoline and diesel fuels based on renewable resources, such as corn-based ethanol and bio-diesel. Most bio-diesels are based on cash crops, such as soybeans, which require a significant amount of energy to grow and harvest. Moreover, the cash crops themselves must be devoted to the production of bio-diesel.
Research conducted from 1980-1996 by the U.S. Department of Energy established algae as a source of bio-diesel. Biofuel is produced by digestion for methane or hydrogen fuels, lipid extraction for bio-diesel and distillation for ethanol. Unlike the other forms of bio-diesel fuel, the production of the algae itself is utilitarian—wastewater treatment being a prime example. In addition to its benefits as a precursor to biofuels, algae has been developed for other uses, such as an organic fertilizer in lieu of the more expensive and increasingly scarce nitrogen fertilizers. Collected algae biosolids has even been proposed as a basis for an alternative textile, for high value chemicals such as medicines, and for nutritional additives especially for animal feed.
Biodiesel has been investigated by the U.S. Department of Energy as part of its “Aquatic Species Program” that began in 1978. Funding for this program was eliminated in 1995, but growing concerns over non-renewable fossil fuels has prompted growing interest in this seemingly infinite and renewable source for diesel fuel. The DOE's approach has been to create algae ponds or “raceways” near factories that generate waste CO2. The waste CO2 and other nutrients are injected into water circulating around a racetrack shaped pond. Algae growing in the circulating water feeds on the CO2. The algae is eventually diverted from the pond for further processing as a biofuel. Thus, the DOE focus has been on artificially creating a growing environment for algae by recycling waste CO2 from a factory or a coal-fired power plant. Of course, one significant limitation of this technology is that it is tied to a source of waste CO2. Another detriment is that this proposed technology requires a large raceway pond, and ultimately a large amount of dedicated land in order to support enough algae to accept the waste CO2 and to produce a meaningful amount of algae for use in making a biofuel. Since the algae requires exposure to sunlight for growth, the ponds must be shallow, which means that the surface area of the pond must be very large to support the algae colonies. The large size of the pond also means that the useful “season” may be limited in certain locales and climates due to freezing of the pond.
The present invention capitalizes on this multiple functionality of algae—especially on algae's role as a catalyst for biologically treating wastewater and as a source of biofuel—while eliminating the significant problems associated with prior algae-based waste treatment systems.